An oldie but goodie TED Talk. These are consistently the most engaging and interesting speeches. FYI I run a video site called Chime.TV and we created a channel just for TED Talks: http://chime.tv/tedtalks

Recent ones I've enjoyed are Erin McKean's Redifining The Dictionary ( http://chime.tv/tedtalks/3l9sg ) and Rives: Is 4AM The New Midnight? ( http://chime.tv/tedtalks/2gdlw )